There are a number of applications in which conversion is required between DC power and AC power. The applicants earlier International patent applications PCT/AU2011/000985, PCT/AU2012/000964 and PCT/AU2015/050315, describe such systems having improved methods of performing this conversion.
The systems described provide for creation of an AC signal suitable for power supply or injection into mains power from DC sources consisting of a string of modules each connected to a DC power source. The modules are transitioned in an out of series in order to form an AC signal or in order to form a stepwise approximation of an AC signal with further ramping being performed to allow the signal to more closely resemble a smooth AC signal.
One issue with such a system relates to determining which modules should be transitioned in or out of series in order to achieve reliable and efficient AC power supply or mains grid current injection.
Poor Electromagnetic Compatibility (EMC) can lead to interference with close by or connected devices and poor harmonic quality of the AC signal can lead to undue heating and interference with connected devices.
An issue with such a system relates to stable control and the operation of the modules as they are transitioned into and out of the series circuit such that levels of Electromagnetic Compatibility (EMC) and harmonics remain acceptable.
It is desired to have a system that is suitable for creating AC signals for stand-alone or grid power injection applications.
The present invention relates to an improved system and method for conversion of DC to AC power aimed at addressing, at least in part, the abovementioned issues.